This invention relates to a flexible disk drive and, in particular, to a position detection unit for use in the positioning of a carriage for supporting a magnetic head and for use in aligning itself.
As is well known in the art, a flexible or floppy disk drive (which may be abbreviated "FDD") of the type described is a device for carrying out data recording and reproducing operation to and from a magnetic disk medium of a flexible or floppy disk (which may be abbreviated to "FD") which has been loaded therein. The flexible disk drive is one of the disk-exchangeable type of magnetic disk drives because the flexible disk to be loaded therein is exchangeable. In recent years, FDs have been significantly improved to have a greater storage capacity. Specifically, development has been made of FDs which have a storage capacity of 128 Mbytes (which may be called large-capacity FDs) in contrast with the FDs having storage capacity of 1 Mbyte or 2 Mbytes (which may be called small-capacity FDs). Following such development, the FDDs have also improved so that they also accept the large-capacity FDs for data recording and reproducing operations to and from the magnetic disk media of the large-capacity FDs.
Throughout the present specification, FDDs capable of recording/reproducing data for magnetic disk media of the large-capacity FDs alone will be referred to as high-density exclusive type FDDS. On the other hand, FDDs capable of recording/reproducing data for magnetic disk media of the small-capacity FDs alone will be called low-density exclusive type FDDs. Furthermore, FDDs capable of recording/reproducing data for magnetic disk media of both the large-capacity and the small-capacity FDs will be called high-density/low-density compatible type FDDs. In addition, the high-density exclusive type FDDs and the high-density/low-density compatible type FDDs may collectively be called high-density type FDDs.
A main difference on mechanism between the low-density exclusive type FDD and the high-density type FDD is a structure of a driving arrangement for moving a carriage supporting a magnetic head along a predetermined radial direction for the magnetic disk medium of the FD loaded in the FDD. More specifically, the low-density exclusive type FDD uses a stepping motor as the drive arrangement. On the other hand, the high-density type FDD uses a linear motor such as a voice coil motor (which may be abbreviated to "VCM") as the drive arrangement.
Now, description will be made in detail as regards the voice coil motor used as the drive arrangement in the high-density type FDD. The voice coil motor comprises a voice coil and a magnetic circuit. The voice coil is disposed on the carriage at a rear side and is wound around a drive axis extending in parallel to the predetermined radial direction. The magnetic circuit generates a magnetic field in a direction intersecting that of an electric current flowing through the voice coil. With this structure, by causing the electric current to flow through the voice coil in a direction intersecting that of the magnetic field generated by the magnetic circuit, a drive force occurs in a direction extending to the drive axis on the basis of interaction of the electric current with the magnetic field. The drive force causes the voice coil motor to move the carriage in the predetermined radial direction.
As well known in the art, the FD includes a magnetic disk medium accessed by a magnetic head. The magnetic disk medium has a plurality of tracks for recording data in the form of concentric circles. As a matter of course, the large-capacity FD is smaller than the small-capacity FD in track width and/or track pitch. The tracks include the most radially outer circumference track (which is named "Tr00") and the most radially inner circumference track. The most radially outer circumference track Tr00 is herein called the most end track. The small-capacity FD has eighty tracks from the most radially outer circumference track Tr00 to the most radially inner circumference track Tr 79 at one side.
It is necessary to position the magnetic head at a desired track position in a case where the FD is accessed by the magnetic head in the FDD. For this purpose, the carriage for supporting the magnetic head must be positioned.
In the low-density exclusive type FDD using the stepping motor as the driving arrangement, it is possible to easily carry out the positioning of the carriage. This is because the stepping motor makes the carriage move step by step in response to pulses applied thereto in the low-density exclusive type FDD. Accordingly, it is unnecessary for the low-density exclusive type FDD to be provided with any exclusive positioning arrangement apart from the stepping motor.
On the other hand, in the high-density/low-density compatible type FDD using the linear motor as the driving arrangement, it is necessary to be provided with the exclusive positioning arrangement for positioning the carriage in a case that the low-density FD is loaded in the high-density/low-density compatible type FDD. This is because the linear motor makes the carriage freely move along the predetermined radial direction on the basis of current flowing in the coil and it is therefore necessary to carry out any control to stop the free movement of the carriage. In order to position the carriage, it must be provided with a position detection unit for detecting a current position of the carriage or the magnetic head and a control unit for controlling the position of the carriage on the basis of the current position detected by the position detection unit.
By the way, it is unnecessary to use the position detection unit in a case that the high-density FD is loaded in the high-density/low-density compatible type FDD. This is because the high-density FD has servo control data which is recorded on the magnetic disk medium thereof.
In addition, it is necessary to detect the position corresponding to the most radially outer circumference track Tr00 of the magnetic disk medium in a case that the low-density FD is loaded in each of the low-density exclusive type FDD and the high-density/low-density compatible type FDD. Moreover, it is necessary to adjust a position (or alignment) of the position detection unit when each of the low-density exclusive type FDD and the high-density/low-density compatible type FDD is assembled. The alignment adjustment is called off-track adjustment in this field.
The off-track adjustment is carried out by the use of an adjusting medium which is called an alignment disk. The alignment disk has a most radially outer circumference track Tr00, a most radially inner circumference track Tr 79, and an alignment adjusting track that standard signals are recorded on, respectively. The alignment adjusting track is halfway between the most radially outer circumference track Tr00 and the most radially inner circumference track Tr 79. Generally, a track Tr40 is selected and used as the alignment adjusting track.
A position detection unit is proposed by Applicants in U.S. patent application Ser. No. 08/792,986. The proposed position detection unit comprises a scale mounted on a carriage for supporting a magnetic head and a photointerrupter mounted on a substrate located close to a main frame. The position detection unit detects both a carriage position representative of a position of the carriage and a most end position corresponding to a most radially outer circumference track of a magnetic disk medium loaded in a flexible disk drive.
Referring to FIG. 1, a scale for use in a position detection unit proposed by Applicants in U.S. patent application Ser. No. 08/792,986 will be described in order to facilitate an understanding of the invention.
The scale 31' has a plurality of light transmission/shield elements 311 which are equally spaced along a direction in parallel with a predetermined radial direction B of a magnetic disk medium of a flexible or floppy disk (FD) loaded in a magnetic disk drive (FDD). In the example being illustrated, the scale 31' is made of an opaque member. The light transmission/shield elements 311 are slits bored through the scale 31'. The light transmission/shield elements 311 are used for detecting a position of a carriage which supports a magnetic head of the FDD. The scale 31' has an additional light transmission/shield element 312' which is an opening window bored through the scale 31' at a lower side. The additional light transmission/shield element 312' is used for detecting a most outer circuit circumference track Tr00 of the magnetic disk.
The scale 31' is used for off-track adjustment together with a photointerrupter. However, the off-track adjustment takes a long time because the scale is of no use to detect an alignment adjusting track of an alignment disk which is used for the off-track adjustment.
The scale has a plurality of slits for detecting the carriage position and a notch for detecting the most end position. The slits are spaced along a direction in parallel with a predetermined radial direction. The photointerrupter has a light-emitting unit and a light-receiving unit which are arranged opposite to each other so that the scale is interposed with spaces between the light-emitting unit and the light-receiving unit. The light-emitting unit has first and second light-emitting sections corresponding to the slits and the notch, respectively. Similarly, the light-receiving unit has first and second light-receiving sections corresponding to the slits and the notch, respectively.
Off-track adjustment is carried out to be attached to the flexible disk drive as follows. First, the photointerrupter is temporarily placed on the substrate and the scale is fixed to the carriage. In this situation, the carriage is moved along the radial direction to detect the standard signal recorded on the most radially outer circumference track Tr00 by the use of the magnetic head. Then, the photointerrupter is adjusted in position and is temporarily fixed on the substrate so as to detect the most end position by the use of the scale in a state that the magnetic head detects the standard signal recorded on the most radially outer circumference track Tr00. Next, the carriage is moved toward an inner circumference side along the radial direction to detect the standard signal recorded on the alignment adjusting track Tr40 by the use of the magnetic head. If the carriage position detected by the photo-interrupter is different from an actual position of the carriage when the magnetic head detects the standard signal recorded on the alignment adjusting track Tr40, the photointerrupter is adjusted in position again so that the carriage position coincides with the alignment adjusting track Tr40.
The position detection unit is available for the off-track adjustment as mentioned above. However, it takes a long time for the magnetic head to detect the alignment adjusting track Tr40 even though the position detection unit is used for the off-track adjustment. This complicates assembly of the flexible disk drive.